Pyridine mediated transition-metal-free direct alkylation of anilines using alcohols via borrowing hydrogen conditions

Abstract

Herein, we report aza-aromatics based organic mediators as a readily accessible alternative to the traditional approach of using transition metal catalyst systems for the activation of alcohols in borrowing hydrogen reactions.

Silver/manganese dioxide nanorod catalyzed hydrogen-borrowing reactions and tert-butyl ester synthesis

“…Based on these experiments and the work of other groups, 33–35 we propose a tentative mechanism for the hydrogen-borrowing reaction (Scheme 2). First, the alcohol is oxidized to an aldehyde via dehydrogenation by the Ag@MnO 2 .…”

“…Therefore, these control experiments imply that radicals are not involved in the hydrogen-borrowing reaction, but that they are involved in the synthesis of tertbutyl esters. Based on these experiments and the work of other groups, [33][34][35] we propose a tentative mechanism for the hydrogen-borrowing reaction (Scheme 2). First, the alcohol is oxidized to an aldehyde via dehydrogenation by the Ag@MnO 2 .…”

“…As for the reaction of the arylcyanide with TBHP, we inferred from the control experiment that it proceeded via a radical pathway. Although the exact mechanism is still unclear, based on the literature 33,34 and the control experiments, we have proposed a tentative mechanism (Scheme 3). According to the previous work, 35 it is possible to generate tert-butoxyl and tert-butylperoxy radicals in this system.…”

“…In addition, Ag nano particles have been shown to have outstanding ability as catalyst in many organic reactions. [30][31][32][33] Based on our recent discoveries on hydrogen-borrowing reactions [34][35][36][37][38] and the properties of manganese oxides (MnO 2 ) nanorods and Ag nanoparticles, we herein report the synthesis and application of Silver/manganese dioxide (Ag@MnO 2 ) nanorods as a catalyst, which has higher catalytic activity after several cycles and which is much cheaper than other catalysts. The Ag@MnO 2 nanorods are characterized by several physical techniques.…”

Mimicking transition metals in borrowing hydrogen from alcohols

“…However, the transition metal-free borrowing of hydrogen from alcohols which mimics transition metals by storing it in a catalyst has not been realized although such attempts have been reported in the literature in which the hydride was stored in the transition metal free catalyst backbone while the proton was stored separately. [36][37][38] Nevertheless, the signature of the borrowing hydrogen mechanism considers the formation of aldehyde and imine as intermediates in the reaction medium. Interestingly, we noticed the formation of aldehyde and imine intermediates during time dependent NMR studies (supported by 1 H NMR peaks at d 10.02 ppm and d 8.46 ppm, Fig.…”